Question: At the market, $5$ light bulbs cost $\$9$. How much do $7$ light bulbs cost? $\$ $
Answer: We're trying to find the cost of $7$ light bulbs. $1$ $\longrightarrow$ $\$1.80$ ${5}$ $\longrightarrow$ ${\$9.00}$ $ \div 5\ $ $ \div 5\ $ ${light bulbs}\ \ \ $ $\longrightarrow$ ${ cost}$ If $C{5}$ light bulbs cost ${\$9}$, then $1$ light bulb costs $\$1.80$. $7}$ $\longrightarrow$ ${\$12.60}$ $1$ $\longrightarrow$ $\$1.80$ $ \times 7\ $ $ \times 7\ $ ${5}$ $\longrightarrow$ ${\$9.00}$ ${light bulbs}\ \ \ $ $\longrightarrow$ ${ cost}$ So, ${7}$ light bulbs cost ${\$12.60}$.